JP2963602B2 - Synchronous rectifier converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous rectifier converter, and more particularly to a synchronous rectifier converter which can be used in parallel with another DC power supply.

[0002]

2. Description of the Related Art Conventionally, a digital rectification circuit using a synchronous rectification circuit of this kind has been proposed.
As shown in FIG. 3, the C-DC converter converts a DC voltage of a DC input power supply 1 into a rectangular pulse voltage by a switching operation of a semiconductor switch 2, and converts the rectangular pulse voltage to a desired voltage by a transformer 3. After that, a rectifying circuit of a rectifying element (synchronous rectifying FET) 4 and a diode 5, a choke coil 6 and a capacitor 7
Rectified and smoothed by a smoothing circuit, and taken out as an average voltage. The switching operation of the semiconductor switch 2 is controlled by a voltage detection control circuit 8 that detects the output voltage of the synchronous rectifier converter.
Control is performed based on the detection status. Incidentally, diodes are used for the rectifying elements 4 and 5 in a normal converter. However, the synchronous rectifying converter of the present invention employs a single-side synchronous rectifying system in which only a rectifying side is replaced with a field effect semiconductor switch (FET) as a synchronous rectifying circuit. It is intended for. Such synchronous rectifier converters are available in a large number of models from small capacity to large capacity so as to correspond to the load capacity, and a synchronous rectifier converter corresponding to the load capacity is selected and used.

[0003]

However, preparing a synchronous rectifier converter in accordance with the load capacity means increasing the number of models, and requires inventory for each model. It is desired to reduce the number of models from the viewpoint of design, production and article management, and it is being studied to cope with large-capacity loads by connecting the same model in parallel, but the conventional synchronous rectifier converter shown in FIG. When used in parallel connection or when another DC power supply (battery or the like) is used in parallel, the following problems occur.

That is, when another synchronous rectifier converter of the same kind or an external DC power supply 11 such as a battery is connected in parallel to the output terminals 9 and 10 as described above, the other power supply connected in parallel is used. However, when the voltage is relatively higher than the output voltage of the synchronous rectifier converter and the voltage detection control circuit 8 detects this, and stops the operation of the semiconductor switch 2, or when the synchronous rectifier converter has a protection device. When the power supply is stopped due to the operation of
0, the voltage of the external DC power supply 11 is supplied and applied to the gate of the synchronous rectification FET 4, and the synchronous rectification F
The conduction state of ET4 will be continued. This is because, when an FET is used as a synchronous rectifying element, if the bias of the gate is normal to the source potential, a current can flow between the drain and source of the synchronous rectifying FET 4 in either direction. The current may flow backward from the output terminals 9 and 10 and eventually be destroyed. According to the present invention, the synchronous rectifier converter is brought into an inoperative state, for example, when the voltage of the external DC power supply 11 connected in parallel to the output terminals 9 and 10 becomes higher than the output voltage of the synchronous rectifier converter of the main body. The present invention also provides a synchronous rectifier converter in which the synchronous rectification FET 4 is not turned on by the external DC power supply 11 even in such a case.

[0005]

SUMMARY OF THE INVENTION A synchronous rectifier converter according to the present invention converts a DC input voltage into a rectangular wave pulse voltage by a switching element and applies it to a primary winding of a transformer. In a synchronous rectifier converter that rectifies and smoothes the extracted desired voltage pulse by using a synchronous rectification FET, a diode, a choke coil, a capacitor, etc., and outputs a DC voltage, the synchronous rectification FET
The control terminal is connected to the connection point between the secondary winding of the transformer and the drain of the synchronous rectification FET so that the synchronous rectification FET operates at a voltage having a polarity opposite to the operating voltage polarity of the synchronous rectification FET. A control element for controlling the operation of the FET is provided so that the control element and the synchronous rectification FET are not operated by an external DC power supply connected in parallel to the synchronous rectification converter.

[0006]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and the same parts as those of the conventional example shown in FIG. In this embodiment, the gate of the synchronous rectification FET 4 is connected to the control FET 12 which operates with the polarity opposite to the operation polarity of the synchronous rectification FET 4. That is, synchronous rectification F
When ET4 uses an n-channel FET, control F
A p-channel FET will be used for ET12. And the control FET is connected to the gate of the synchronous rectification FET4.
The source terminal of the control FET 12 is connected to a connection point between the commutation diode 5, the choke coil 6, and the secondary winding of the transformer 3. The gate terminal of the control FET 12 is connected to the other terminal of the secondary winding of the transformer 3.

With such a connection configuration, the gate and the source of the p-channel control FET 12 are connected between the secondary windings of the transformer 3, so that the voltage is applied to the secondary windings in a direction in which a positive bias is applied. Control FET only when
12 operates, whereby the synchronous rectification FET 4 conducts. That is, when no positive bias voltage is generated in the secondary winding, the synchronous rectification FET 4 does not conduct. Therefore, even if the voltage of the external DC power supply 11 is applied to the output terminals 9 and 10, the voltage is not the voltage of the operation polarity of the control FET 12, so that the control
Since the ET 12 does not operate, the synchronous rectification FET 4 does not operate. That is, even when the synchronous rectifier converter is in a stopped state or a voltage drop state, the external DC power supply 11 does not operate the synchronous rectification FET 4 and no reverse current flows from the output terminal.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and the same parts as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals. In the embodiment shown in FIG. 2, diodes 16 and 17 are connected in series between the drain and the source of the synchronous rectification FET 4, and the connection point of both diodes is connected to the gate of the control FET 12. In the embodiment shown in FIG.
During operation of the synchronous rectifier converter, the voltage applied to the gate of the control FET 12 is applied to both positive and negative polarities of the voltage generated in the secondary winding of the transformer 3, but in this embodiment, only the positive voltage is applied. The amount of charge for charging and discharging the gate is greatly reduced.

In this embodiment, similarly to the embodiment shown in FIG. 1, even if the voltage of the external DC power supply 11 is applied to the output terminals 9 and 10, the voltage is not the operating polarity of the control FET 12. Since the control FET 12 does not operate, the synchronous rectification FET 4 does not operate. In the embodiment shown in FIGS. 1 and 2, when no voltage is generated in the transformer 3, the synchronous rectification FET 4 and the control FET 12
In order to prevent the impedance of the gate circuit from becoming high, the resistors 14 and 18 and the diode 15 are provided. Further, although the FET is used as the control element for controlling the operation of the synchronous rectification FET 4 in both embodiments, the control can be performed using a normal transistor.

[0010]

As described above, according to the present invention, the synchronous rectification FET of the present synchronous rectifier converter has a
It operates only by the square wave pulse voltage generated on the secondary side, and prevents the synchronous rectification FET from being operated by the external DC power supply connected in parallel to the synchronous rectification converter, thereby enabling the parallel connection operation of the external DC power supply. In particular, a synchronous rectifier converter of the same type can be connected in parallel according to the load capacity, and has an effect of reducing the number of synchronous rectifier converters in addition to the safety of operation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a synchronous rectifier converter according to the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the synchronous rectifier converter according to the present invention.

FIG. 3 is a circuit diagram of a conventional one-side synchronous rectification type synchronous rectification converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC input power supply 2 Semiconductor switch 3 Voltage conversion transformer 4 Synchronous rectification FET 5,13,15,16,17 Diode 6 Choke coil 7 Capacitor 8 Voltage detection control circuit 9,10 Output terminal 11 External DC power supply 12 Control FET 14,18 resistance

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naoki Murakami 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (58) Field surveyed (Int. Cl. ⁶ , DB name) H02M 3 / 28 H02M 7/21

Claims (2)

(57) [Claims] 1. A DC input voltage is converted into a rectangular wave pulse voltage by a switching element, applied to a primary winding of a transformer, and a desired voltage pulse extracted by a secondary winding of the transformer is converted to a synchronous rectification FET. Rectifier, rectifier and smoother with a diode, a choke coil, a capacitor, etc., and outputs a DC voltage.
The control terminal is connected to the connection point between the secondary winding of the transformer and the drain of the synchronous rectification FET so that the synchronous rectification FET operates at a voltage having a polarity opposite to the operating voltage polarity of the synchronous rectification FET. A synchronous rectifier converter comprising a control element for controlling operation of an FET. 2. The method according to claim 1, wherein a plurality of diodes are connected in series between a drain and a source of the synchronous rectification FET, and an interconnection point of the plurality of diodes is connected to a control terminal of the control element. The synchronous rectifier converter according to claim 1, wherein